In applications where materials such as paint are applied by hand using an electrostatic spray gun, spray guns having internal power supplies are becoming increasingly popular. One reason for their popularity is that the guns are safer and easier to use than prior art electrostatic hand guns which require a heavy insulated high voltage wire. In a typical hand held electrostatic spray gun with an internal power supply, the power supply consists of two modules. In a first module, a low voltage direct current is converted to an alternating current by an oscillator. A voltage step-up transformer may be located in either the first or the second modules for increasing the voltage of the alternating current from the oscillator. The second module includes a voltage multiplier which rectifies and multiplies to a high voltage the output from the transformer. The voltage multiplier is typically a ladder or cascade network formed from capacitors and diodes.
Typical prior art hand held spray guns of this type are shown in U.S. Pat. No. 4,598,871 to Hartle, U.S. Pat. No. 4,750,676 to Huber et al. and U.S. Pat. No. 4,752,034 to Kuhn et al. In the spray guns in each of these patents, a circuit module for the high voltage power supply is located within the handle for the spray gun. During operation of the spray gun, the power supply will produce heat in addition to the high voltage. If the spray gun is used for an extended period of time, the handle may become sufficiently hot to be uncomfortable to the operator. The high temperature also may adversely affect the circuit components in the circuit module.